The invention relates to continuously variable transmissions (CVT) of the type employing rotary input and output shafts, adjustable pulleys on the shafts, and an endless flexible element (such as an endless flexible chain or belt and hereinafter called chain for short) which is trained over the pulleys. Transmissions of such character are preferred by numerous makers of motor vehicles or power trains for use in motor vehicles because they exhibit important advantages over other types of continuously variable transmissions, e.g., those which employ planetary gears. Thus, the ride in a motor vehicle comprising a power train embodying a continuously variable transmission which comprises input and output shafts with adjustable pulleys and an endless chain trained over the pulleys is more comfortable to the operator and other occupants of the motor vehicle, and the engine can be operated with considerable savings in fuel consumption.
Published German patent application Serial No. 195 44 644 A1 discloses a continuously variable transmission with two adjustable pulleys and an endless chain which serves to transmit torque from the adjustable pulley on the input shaft to the adjustable pulley on the output shaft. Each pulley comprises a first flange which is fixedly secured to the respective shaft, and a second flange which cannot rotate with reference to the respective shaft but is movable axially toward and away from the associated fixed flange. First plenum chambers are provided at those sides of the axially movable flanges which face away from the associated first flanges. The pressure of a hydraulic fluid in such chambers is regulated in dependency upon the magnitude of the torque being transmitted to the input shaft at any given time. Such mode of operation is desirable because it ensures that the chain cannot slip, or is less likely to slip, relative to the adjacent surfaces of the flanges. Changes in the ratio of the transmission are effected by changing the pressure of fluid in additional plenum chambers which are outwardly adjacent the respective first plenum chambers. A torque sensor is integrated into the just described conventional transmission to monitor the magnitude of the torque being transmitted from a prime mover (such as an internal combustion engine) to the input shaft of the transmission.
As a rule, and as already mentioned hereinbefore, the first plenum cambers are located between the additional plenum chambers and the axially movable flanges of the respective pulleys. The arrangement is normally such that each first plenum chamber is immediately adjacent the respective axially adjustable flange. On the other hand, the additional plenum chambers are immediately adjacent to pistons which are directly connected to the respective axially movable flanges. A third plenum chamber is or can be provided between each first plenum chamber and the respective additional plenum chamber. The third plenum chamber receives and/or discharges hydraulic fluid by way of a throttling orifice, and its purpose is to compensate for those rises of fluid pressure which are attributable to forces developing as a result of rotation of the shafts and pulleys when the transmission is in use. However, the utilization of such third plenum chambers results in considerable pumping losses because of uninterrupted flow of pressurized fluid from the first plenum chambers. In addition, the third plenum chambers impose a lower limit upon the duration of changes of the transmission ratio. The reason is that, when the volume of a third chamber is being reduced, some of the fluid must be expelled from the third chamber into the atmosphere by way of one or more narrow flow restrictors which impose a lower limit upon the speed of adjustment of the transmission ratio.
The aforementioned published German patent application Serial No. 195 44 644 A1 further discloses a hydromechanical torque sensor which is installed to transmit to the pulley on the input shaft the entire torque being supplied by a prime mover. More specifically, the torque sensor comprises an axially fixed first cam and an axially movable second cam, and the cams are provided with confronting ramps engaging spherical distancing or spreading members which are disposed between the two cams. The second cam is movable axially of but cannot rotate relative to the input shaft of the transmission. It is necessary to ensure that the pressure of hydraulic fluid in the first plenum chambers is variable at least as a function of the transmitted torque; this ensures that the flanges bear upon the marginal portions of the chain without any or with minimal slip. In other words, if the magnitude of the transmitted torque increases, then the torque sensor must ensure that the fluid pressure in the first chambers increases accordingly. Analogously, if the magnitude of transmitted torque is reduced, the torque sensor initiates a reduction of fluid pressure in the first plenum chambers because the likelihood of slippage between the flanges of the pulley on the one hand, and the marginal portions of the chain on the other hand, is less pronounced. When the transmission ratio reaches a certain value, the first and the adjacent second chambers are permitted to communicate with each other by way of the respective axially movable flanges to thus account for an increased area of contact with the chain, i.e., the pressure of fluid in the first plenum chambers is reduced.
The just outlined construction and mode of operation of the torque sensor which is disclosed in the aforementioned published German patent application ensure that the pressure between the conical surfaces of the flanges and the marginal portions of the chain can be regulated as a function of the momentary transmission ratio, i.e., of the radii of those arcuate portions of the endless chain which are trained over the two pulleys. This renders it possible to ensure that the torque sensor operates not unlike a multistage torque sensor.
However, the just described torque sensor also exhibits certain drawbacks. For example, the space requirements of the torque sensor, as seen in the axial direction of the input shaft, are rather pronounced which is evidently undesirable in many types of motor vehicles. Moreover the torque sensor is quite complex and comprises a rather substantial number of component parts.
Published German patent application Serial No. 42 01 692 A1 discloses a continuously variable transmission which comprises a dual cylinder-and-piston arrangement wherein the axially movable flange of each of the two pulleys is associated with a double-acting cylinder and piston unit, and such units are radially offset relative to each other. The arrangement is such that each cylinder-and-piston unit can furnish a fluid at a desired pressure, i.e., each of the units can pressurize the fluid to a desired extent independently of the pressure in the other unit. Thus, the radially inner plenum chamber contains a body of fluid the pressure of which is just sufficient to ensure the transmission of a desired torque from the pulley on the input shaft to the pulley on the output shaft. On the other hand, the fluid in the radially outer cylinder-and-piston units is pressurized only when the transmission ratio must be changed, i.e., if the ratio of the transmission is to be changed in actual use, e.g., in the power train of a motor vehicle.
Another feature of the continuously variable transmission which is disclosed in the published German patent application Serial No. 42 01 692 A1 is that the running endless flexible chain contributes to an increase of the force acting between such endless chain and the flanges of the pulley on the input shaft of the transmission. Such force is compounded by the force which is furnished by pressurized fluid in the second plenum chambers.
Further double-acting cylinder and piston units are disclosed in published German patent application Serial No. 41 33 724 A1. The two plenum chambers which are associated with each axially movable flange are axially offset relative to each other and are free to communicate with one another, i.e., the axial forces attributable to the provision of such plenum chambers which communicate with one another are compounded.
The disclosures of all patents and patent applications which are identified in the specification of the present application are incorporated herein by reference.
An object of the instant invention is to provide a continuously variable transmission which is designed in such a way that its ratio can be changed within short intervals of time.
Another object of the invention is to provide a relatively simple, compact and inexpensive continuously variable transmission which can be utilized as a superior substitute for the aforedescribed conventional continuously variable transmissions.
A further object of the invention is to provide a continuously variable transmission which takes up a surprisingly small amount of space in the axial direction of its input and output shafts.
An additional object of the invention is to provide a continuously variable transmission wherein the number of separately produced parts is small or even negligible in comparison with the number of constituents of a conventional continously variable transmission of the type employing parallel input and output shafts, an adjustable pulley on each shaft, and an endless flexible chain trained over the pulleys.
Still another object of the invention is to provide a novel and improved torque sensor for use in the above outlined continuously variable transmission.
A further object of the invention is to provide a torque sensor which is superior to those utilized in presently known continuously variable transmissions with hydrokinetic torque converters.
Another object of the invention is to provide a novel and improved power train which can be utilized in a motor vehicle and employs a continuously variable transmission of the above outlined character.
An additional object of the invention is to provide a novel and improved array of fluid-confining chambers for use in the above outlined transmission.
A further object of the invention is to provide a novel and improved method of assembling and operating a continuously variable transmission of the above outlined character.
Still another object of the invention is to provide novel and improved constituents of a continuously variable transmission.
An additional object of the invention is to provide novel and improved means for moving the axially movable flanges relative to axially fixed flanges of pulleys on the input and output shafts of a continuously variable transmission, particularly a transmission which can be utilized in the power train of a motor vehicle and can receive torque from the output element (such as a crankshaft or a camshaft) of an internal combustion engine or another prime mover.
Another object of the invention is to provide novel and improved fluid flow regulating valves which are constituted by portons of the shafts and axially movable flanges of adjustable pulleys in a continuously variable transmission of the above outlined character.
A first feature of the invention resides in the provision of a continuously variable transmission which comprises a first shaft arranged to rotate about a first axis, a first pulley provided on the first shaft, a second shaft which is rotatable about a second axis and is or can be parallel to the first shaft, and a second pulley including a first conical flange affixed to the second shaft and a second conical flange non-rotatably mounted on and movable axially of the second shaft toward and away from the first flange. The transmission further comprises an endless flexible torque transmitting element (such as a belt or chain) which is trained over the two pulleys, and means for moving the second flange of the second pulley toward and away from the first flange of the second pulley. The moving means includes a first piston which is carried by and is held against axial movement relative to the second shaft and defines with the second flange a first annular plenum chamber, a supporting member which is affixed to the second shaft, and a second piston which is affixed to the second flange and defines with the supporting member a second annular plenum chamber. The first and second pistons define a third annular plenum chamber which is disposed between the first and second chambers, as seen in the axial direction of the second shaft. The moving means further comprises discrete first, second and third means for respectively connecting the first, second and third chambers with at least one source of pressurized hydraulic fluid, and means (such as a set of valves) for regulating the flow of fluid in the second and third connecting means in such way that the pressure of fluid in one of the second and third chambers is reduced simultaneously with a rise of fluid pressure in the other of the second and third chambers.
The second flange of the second pulley can include a cylindrical portion which is remote from the axis of the second shaft, and a hub which surrounds the second shaft. The first piston can be mounted for movement axially of the second shaft between the cylindrical portion and the hub of the second flange, and the supporting means can include a cylindrical wall which is coaxial with and is spaced apart from the second shaft and has an end portion affixed to the first piston. The second piston is movable with the second flange axially of the second shaft and relative to the cylindrical wall of the supporting means, and the third connecting means can include a first channel provided in the supporting member and a second channel provided in the second shaft.
The first pulley preferably comprises a third conical flange affixed to the first shaft, and a fourth conical flange which is non-rotatably mounted on and is movable axially of the first shaft toward and away from the third flange. Such transmission preferably further comprises fluid-operated means (e.g., a cylinder and piston arrangement) including a fourth chamber and serving to move the fourth flange relative to the third flange.
The just described transmission can further comprise means (e.g., a connection between the rotary output element of the engine and the first flange of the second pulley) for rotating the second shaft. The endless flexible element is then arranged to transmit torque from the second shaft to the first shaft. The aforementioned fluid-operated means can include means for maintaining the pressure of fluid in the fourth chamber at a value which at least approximates the fluid pressure in the first chamber and is a function of the magnitude of torque being transmitted by the endless flexible torque transmitting element.
Another feature of the present invention resides in the provision of a torque sensor which can be utilized in a continuously variable transmission having an input shaft, a pulley including a first flange which is affixed to the shaft and a second flange which is non-rotatably mounted on and is movable axially of the shaft toward and away from the first flange, and an endless flexible element trained over the pulley. The improved torque sensor comprises first and second cams which are coaxial with the input shaft and have confronting surfaces provided with complementary ramps, at least one (e.g., spherical) spreading element disposed between and contacting the complementary ramps, and a gear which is coaxial with and is rotatably mounted on the input shaft. The second cam is non-rotatably and axially movably mounted on the gear, and the torque sensor further comprises an annular piston which surrounds the input shaft, which abuts the second cam and which is movable axially of the input shaft. The second cam has a side facing away from the first cam, and the torque sensor further comprises first and second plenum chambers which spacedly surround the input shaft and one of which is nearer to the shaft than the other chamber (as seen in the radal direction of the shaft. Still further, the torque sensor comprises a substantially disc-shaped member which forms part of the first cam, which is made at least in part of sheet metal, which is non/rotatably affixed to the first flange, and which includes a substantially cylindrical portion surrounding the two chambers and the second cam. The first cam further includes an intermediate portion extending from the substantially cylindrical portion toward the input shaft; the at least one spreading element is disposed between the intermediate portion of the first cam and the second cam.
The piston is preferably configurated and mounted in such a way that it has a side which faces the first flange of the pulley and is provided with a first annular extension extending toward the first flange and spacedly and concentrically surrounding the input shaft. The first flange preferably includes a second annular extension and the one plenum chamber (namely the chamber nearer to the axis of the input shaft) is bounded by a peripheral surface of the input shaft, by the first annular extension (of the piston) and by the first flange. The substantially cylindrical portion of the first cam has an internal surface which confronts the periphery of the input shaft and serves to guide a radially outer portion of the piston for movement in the direction of the axis of the input shaft. The other plenum chamber (namely the chamber which is more distant from the axis of the input shaft) is bounded by the substantially cylindrical portion of the first cam, by the piston, by the second extension (of the first flange) and by another part of the first flange.
The radially outer portion of the piston can be provided with a sealing element (e.g., an O-ring) which abuts the internal surface of the substantially cylindrical portion of the first cam. Such sealing element can be received in a circumferential groove of the radially outer portion of the piston.
It is desirable to install an annular sealing element between the annular extension of the piston and the annular extension of the first flange; such sealing element can be received in a groove of one of the two annular extensions, e.g., in the annular extension of the first flange.
The first cam can be configurated and mounted in such a way that it comprises an end portion extending substantially radially outwardly from the substantially cylindrical portion and including suitable protuberances in the form of lugs, fingers or the like. The first flange then preferably comprises an annular projection which is adjacent the end portion of the first cam and is coaxial with the input shaft; this projection is provided with recesses for the protuberances on the aforementioned end portion of the first cam. Such torque sensor preferably further comprises a sealing element which is interposed between the first flange of the pulley and the end portion of the first cam; this sealing element can be received in an annular groove of the first flange.
An internal surface of the annular projection of the first flange can be provided with an annular groove for a safety ring (e.g., a detachable split ring) which serves to hold the first cam against axial movement relative to the first flange of the pulley on the input shaft.
The intermediate portion of the first cam can be provided with at least one recess for the at least one spreading element.
The torque sensor further comprises means for moving the second flange of the pulley axially of the input shaft. Such moving means can include at least one hydraulic motor (e.g., a single-acting or double-acting cylinder and piston unit) having at least one additional (third) plenum chamber for a supply of pressurized fluid (e.g., oil), and means for connecting the third plenum chamber with one of the first and second plenum chambers. The connecting means can comprise passages (e.g., in the form of channels, grooves, bores or holes) which are provided in the input shaft and in at least one of the flanges.
The second flange of the pulley can be provided with a control edge (e.g., defined by a circumferentially complete internal annular shoulder) which is adjacent the shaft. The hydraulic motor of the means for moving the second flange relative to the input shaft toward and away from the first flange includes the aforementioned at least one additional or third plenum chamber for a supply of pressurized fluid, and the means for connecting the first and/or second plenum chamber with the third plenum chamber can comprise at least one passage (e.g., a bore) provided in the input shaft and having an open end adjacent the control edge so that the latter can regulate the rate of fluid flow in the at least one passage in response to axial movement of the second flange relative to the shaft.
A further feature of the invention resides in the provision of a continuously variable transmission which comprises an input shaft rotatable about a predetermined axis, and a pulley including a first flange affixed to (e.g., of one piece with) the shaft and a second flange non-rotatably mounted on and movable axially of the shaft toward and away from the first flange. The second flange has a cylindrical portion spacedly surrounding the input shaft and extending away from the first flange (as seen in the axial direction of the input shaft). The transmission further comprises an endless flexible torque transmitting element (chain or belt) which is trained over the pulley, and means for moving the second flange toward and away from the first flange. The moving means comprises a first piston having a section defining with the second flange a first plenum chamber. The first piston has a radially inner portion which is slidable along a radially inner portion of the second flange, and a radially outer portion which is slidable within the cylindrical portion of the second flange. The moving means further comprises a cylinder which is mounted on the input shaft and defines a second plenum chamber with a second piston which is affixed to the second flange. The second plenum chamber surrounds the radially inner portion of the second flange.
The first piston can be provided with an annular trough (e.g., an annular depression in a selected portion of a sheet metal blank which is converted into the first piston in a suitable deforming machine) which is radially outwardly adjacent the aforementioned portion of the second flange, which extends toward the first flange and which includes a cylindrical portion; such cylindrical portion surrounds a radially outer portion of the cylinder.
The transmission can further comprise at least one first sealing element disposed between the cylindrical portion of the second flange and the first piston, and at least one second sealing element between the radially inner portion of the first piston and the radially inner portion of the second flange. The at least one first sealing element can be recessed into the cylindrical portion of the second flange and/or into the first piston, and the at least one second sealing element can be recessed into the first piston and/or into the radially inner portion of the second flange.
At least one sealing element can be interposed between the second piston and a cylindrical radially outer portion of the cylinder; such sealing element can include a ring which is recessed into the cylinder and/or into the second piston.
In accordance with a presently preferred embodiment, the transmission further comprises novel and improved means for admitting oil or another suitable pressurized hydraulic fluid into the second plenum chamber. Such admitting means can include at least one first passage which is provided in the input shaft, and at least one second passage provided in the radially inner portion of the second flange. The at least one second passage communicates with the at least one first passage in at least one predetermined axial position of the second flange relative to the input shaft.
The means for supplying a pressurized fluid to the first plenum chamber can include at least one first passage provided in the second flange, an internal recess provided in the second flange and communicating with the at least one first passage, and at least one second passage provided in the shaft and communicating with the recess in at least one predetermined axial position of the second flange relative to the input shaft. The recess can constitute a relatively wide circumferentially complete groove in the internal surface of the second flange.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved transmission itself, however, both as to its construction and the modes of assembling and utilizing the same, together with numerous additional important features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.